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Comparativein VitroSkin Absorption and Metabolism of Coumarin (1,2-Benzopyrone) in Human, Rat, and Mouse

https://doi.org/10.1006/taap.1997.8154Get rights and content

Abstract

Thein vitropercutaneous absorption and skin metabolism of coumarin (1,2-benzopyrone) was studied in metabolically viable human, rat (F344), and mouse (CD1 and DBA/2) skin. Following application of [14C]coumarin (3.7 μg/cm2; 0.02% in ethanol) to unoccluded skin in flow-through diffusion cells of a skin absorption model (SAM), the absorption through the skin into the receptor fluid at 72 hr was rapid and extensive in all species, reaching (mean ± SD) 50.4 ± 9.1% of the applied dose in human, 51.3 ± 7.3% in rat, and 44.9 ± 13.5% in mouse. When the skin was occluded immediately after exposure, the extent of absorption at 72 hr was enhanced in all species. At 72 hr, substantial amounts of [14C]coumarin were found in unoccluded mouse skin (31.7 ± 13.6%), with less in human (10.2 ± 6.5%) and rat (12.7 ± 5.0%) tissue. When occluded, the skin residues at 72 hr were 10.4 ± 11.7% (mouse), 8.5 ± 3.9% (human), and 11.9 ± 7.5% (rat). The absorption of coumarin through rat skin into the receptor fluid over 72 hr was linearly related to the applied dose (r2= 0.998 unoccluded skin;r2= 0.999 occluded skin) over the dose range 3.7 to 378.7 μg/cm2. The nature and extent of cutaneous metabolism was studied following (i) topical application for 24 hr to human, rat, and mouse skin in the SAM system; (ii) incubation at 37°C for up to 6 hr with human, rat, and mouse whole skin homogenates; and (iii) incubation at 37°C for up to 24 hr with freshly isolated and cultured human epidermal keratinocytes. HPLC and GCMS analyses of skin extracts and receptor fluid confirmed that, in all three species, only the parent compound, coumarin, was present at all times from 10 min to 24 hr. These data indicate that topically applied coumarin is rapidly and extensively absorbed through human, rat, and mouse skin, and that the compound remains metabolically unchanged during absorption. These observations may have implications for the safe and effective use of coumarin in consumer products which come into contact with the skin and as a topical therapeutic agent.

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      When the same dose is applied to the skin the peak concentration in blood varies. It depends on the rate of absorption characterised by the half-life of absorption and the extent of absorption which we varied both according to the experimental results of Beckley-Kartey et al. (1997), Ford et al. (2001), and Yourick and Bronaugh (1997): extent of absorption (60% and 100%, respectively) and rate of absorption (half-lives between 30 min and 960 min). With similar absorption half-lives (20 min for the oral and 30 min for the dermal absorption), identical doses (0.1 mg/kg) and extent of absorption (100%) the peak concentration after dermal exposure is considerably higher (51 μg/kg blood) as compared to oral exposure (3.1 mg/kg blood) (Fig. 2a and Table 3).

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    R. L. BronaughH. I. Maibach, Eds.

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